This proposal deals with the development of methods to isolate and study the mammalian HGPRT genes. We shall approach the gene isolation through several independent techniques, including plasmid rescue and sib selection. The plasmid rescue method will utilize the ligation of shotgun HGPRT ion human and other mammalian DNA to a plasmid vector such as pBR322, the transformation of HGPRT- mouse cells to HGPRT ion, and the rescue of the plasmid HGPRT recombinant from transformed cellular DNA by restriction enzyme excision. Sib selection techniques will involve the transformation of HGPRT- mouse cells by serial dilutions of clone libraries of human and other mammalian genes. The organization of the HGPRT genes, either structural or regulatory, will be studied by restriction enzyme mapping and nucleotide sequencing, compared with that of the bacterial genes, and the organizational or sequence aberrations in the DNA of patients with the Lesch-Nyhan syndrome and with HGPRT deficient gouty arthritis will be examined.